Moon
Satellite or double planet? The Moon (Latin name: Luna) is Earth's only natural satellite. It is fifth-largest and the second-densest (after Jupiter's satellite Io) natural satellite in the Solar System. The Moon is exceptionally large relative to Earth: a quarter its diameter and 1/81 its mass. It is the largest moon in the Solar System relative to the size of its planet (though Charon is larger relative to the dwarf planet Pluto, at 1/9 Pluto's mass). Earth and the Moon are nevertheless still considered a planet-satellite system, rather than a double planet, because their barycentre, the common centre of mass, is located 1700 km (about a quarter of Earth's radius) beneath Earth's surfaceThis article was adapted from Space Engine's ingame wiki.. Formation The Moon is thought to have formed approximately 4.5 billion years ago, not long after Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. Visibility from Earth The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the second-brightest regularly visible celestial object in Earth's sky (after the Sun), as measured by illuminance on Earth's surface. Although it can appear a very bright white, its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art, and mythology. Distance and apparent size The Moon's gravitational influence produces the ocean tides and the slight lengthening of the day. The Moon's current orbital distance is about thirty times the diameter of Earth, causing it to have an apparent size in the sky almost the same as that of the Sun. This allows the Moon to cover the Sun nearly precisely in total solar eclipse. This matching of apparent visual size is a coincidence. The Moon's linear distance from Earth is currently increasing at a rate of 3.82 ± 0.07 centimetres per year, but this rate is not constant. Moon-map-nearside.jpg|Topographical map of the Moon's near side Moon-map-farside.jpg|Topographical map of the Moon's far side Images The Moon-000.jpg|View of the transition between the Moon's near side and far side The Moon-001.jpg|The far side The Moon-002.jpg|Mare Nectaris, Mare Serenitatis and Mare Humboldtianum and below them the isolated Mare Crisium The Moon-003.jpg|Crescent of the Moon's far side The Moon-004.jpg|Another view of the far side crescent. Near the terminator the Apollo and Oppenheimer craters can be seen The Moon-005.jpg|Close up of the Mare Fecunditatis and the Langrenus Crater. Below it is the Mare Crisium, enclosed by high mountain chains The Moon-006.jpg|Another shot of the Mare Crisium The Moon-007.jpg|Close up of the transition between far and near side The Moon-008.jpg|Close-up of various craters on the far side The Moon-009.jpg|Another close-up of various craters on the far side. Among them the biggest ones are the Rotschild crater on the left and the Rozhdestvensky crater near the middle.. The Moon-010.jpg|Close-up of the polar region The Moon-011.jpg|Mare Serenitatis and Mare Tranquillitatis The Moon-012.jpg|Mare Serenitatis and Mare Imbrium The Moon-013.jpg|The Copernicus and Kepler craters The Moon-014.jpg|The Mare Orientale The Moon-015.jpg|The Leibnitz and Von Karman craters Category:Selenae Category:Objects Category:Real objects Category:Moons